1. Field of the Invention:
The present invention relates to a resistor device for controlling a blower by regulating electric current to be supplied to the blower for adjusting the capacity of the blower.
2. Description of the Prior Art:
In an adjustment of the capacity of an air conditioner, a resistor device is connected between a power supply and a blower motor of a blower for controlling the magnitude of electric current flowing through the blower motor.
The resistor device of the type described includes a plurality of resistors of different resistance values connected in series and selected to vary the magnitude of electric current to be supplied to the blower motor for adjusting the flow rate of the blower. As shown here in FIG. 19 of the accompanying drawings, a blower motor 3 is connected between a power supply 58 and a common terminal 17b' of a resistor circuit 9'. The resistor circuit 9' includes a series of resistors 9a', 9c' and 9d' of different resistance values and connected to terminals 17a', 17c' and 17d', respectively. The terminals 17a', 17c', 17d' are connected through respective thermal fuses 56' to three connecting terminals 29a', 29c', 29d' selected by a switch mechanism 59'. A thermal fuse 56' is connected between the common terminal 17b' and the motor 3. One of the connecting terminals 29a', 29c' and 29d' is selectively connected to the switch mechanism 59' to change the magnitude of a resistance connected in series with the motor 3 to thereby vary the capacity of the motor 3.
When the blower motor 3 is locked under accidental conditions, the resistors 9a', 9c', 9d' generate a great amount of heat due to an overcurrent flowing therethrough. When the temperature of the resistors 9a', 9c', 9e' reaches to a predetermined value, any of the thermal fuses 56' is fused to break down a circuit, thereby stopping power supply to the motor 3.
Since the thermal fuses are placed at an easily accessible position, the user may inadvertently recover the molten thermal fuse by soldering or replacement with a wire for reactivating the resistor device. With the thermal fuse thus recovered, power supply to the motor is not stopped even when an overcurrent flows through a circuit including the motor and the thermal fuse. As a consequence of this overcurrent, the motor is damaged and the circuit is burnt out which may result in a fire.
The thermal fuses 56' stated above have the same melting temperature regardless of the place where the individual thermal fuse is used, as shown, for example, in Japanese Patent Laid-open Publication No. 63-13808. Since the thermal fuse 56' disposed between the common terminal 17b' and the blower motor 3 may be fused in the same manner as the thermal fuses 56' disposed respectively between the resistors 9a', 9c', 9d' and the corresponding connecting terminals 29a', 29c', 29d', it is difficult to determine as to which fuse is melted down.
This means that in the case where one of the thermal fuses 56' at a connecting terminal side is melted down by overcurrent while the thermal fuse 56' at a common terminal side is still alive, a circuit may be completed when the switch mechanism 59' is actuated to another combination of the resistors 9a', 9c', 9d'. In such a case, the circuit including the blower motor 3 is damaged or otherwise burnt out due to overcurrent, which may result in a fire.